The HybriDrive series propulsion system developed by BAE Systems is currently enhancing the fuel efficiency and cutting emissions on more than 3,000 transit buses in cities around the world, including New York and London.

The system is specifically suited to the driving patterns of urban transport, which involve low average speeds and frequent stopping and starting. To meet the needs of applications that have higher operating speeds and less frequent stops, BAE is developing a new parallel hybrid propulsion system to bring the fuel-saving benefits of its technology to medium and heavy-duty trucks.

HybriDrive series propulsion is a diesel-electric system that consists of a generator, an electric motor, and a lithium-ion battery energy storage system that is managed by computerized controls. The diesel engine that turns the generator operates independently of the electric motor, which allows it to run at a nearly constant speed for optimum efficiency. Since the electric motor is what makes the wheels turn, the vehicle also accelerates smoothly with no sudden jerks. Additionally, during braking the electric motor acts as a generator to recapture energy that is stored in the batteries.

While the series propulsion system doesn’t use a transmission – cutting down on maintenance costs – the HybriDrive parallel system integrates a single electric machine between the engine and the transmission. BAE says the system is easy to install and enhances propulsion and lowers fuel consumption and emissions by optimizing the blending of the internal combustion engine power and electric power.